1. Field of the Invention
The present invention is directed to a programmable hearing aid of the type having at least one acoustoelectrical input transducer, a signal processing chain including a signal converter, an amplifier, a digital signal processor and a memory, and an electroacoustical output transducer.
2. Description of the Prior Art
A hearing aid of this type is disclosed in German Auslegeschrift 27 16 336, corresponding to U.S. Pat. No. 4,187,413. In this hearing aid, a microphone is provided as an input signal source that is connected to an amplifier followed by an analog-to-digital converter that is connected to a digital computer stag. A digital-to-analog converter is connected to the output of the computer stage and supplies an analog signal to an output amplifier to which an earphone is connected as an output transducer. The computer stage of this programmable hearing aid can be a microprocessor with a memory and can be implemented as an integrated module. A number of input signals, for example from a microphone and a pick-up induction coil, can thus be correlated with one another in the processor.
Tinnitus is a condition wherein a person perceives noises in the ear or head for which no external causes exist. This can be extremely uncomfortable and can lead to mental and physical disturbance in serious cases. The possibility of alleviating the tinnitus condition by drowning out the tinnitus noise with a sound signal supplied to the ear has been investigated for many years in the scientific literature.
PCT Application WO 90/07251 discloses a tinnitus masking device having an electronic circuit arranged in a housing and an earphone for generating a sound spectrum that can mask the tinnitus of the patient, with a volume control being provided for setting the sound intensity. In this device, the electronic circuit is fashioned such that the sound spectrum generated by the earphone contains a line spectrum with a fundamental tone, and the frequency of the fundamental tone can be set by the user. Tinnitus-masking devices can be either independent devices or can be built into a hearing aid, the combination of a tinnitus masker and a hearing aid being also referred to as tinnitus instrument. This instrument is employed given the appearance of tinnitus and simultaneous hearing loss, which occurs in a great percentage of tinnitus patients. These known devices operate with analog circuits for treating tinnitus or for tinnitus therapy. The tinnitus maskers generate a noise that can be individually adapted for every tinnitus patient in the limited framework to the patient's needs with respect to the frequency and level range. The goal of this therapy is to set the masking noise such that the patient no longer, or only barely, perceives the tinnitus and a more pleasant masking noise is audible instead.
A disadvantage of known tinnitus instruments is that the frequency range and the level range of the masking noise cannot be set with sufficient flexibility. Further, the known type of masking has the disadvantage that it is always in effect and the patient must manually shut the device off if the patient would like to hear normally in certain situations.